The present invention relates to a printing apparatus which executes cross control as control for realizing high-speed printing in, e.g., a serial printer and, more particularly, to an apparatus which employs, as a driving source, a DC motor or ultrasonic motor whose driving profile dynamically changes, and a control method thereof.
In recent years, printers are required to have not only higher image quality but also lower operation noise. Especially, an inkjet printing apparatus which has only a few noise sources in printing uses a DC motor and linear encoder as a driving means for scanning a printhead, thereby reducing noise. Today, a DC motor and rotary encoder are also being employed as a driving means for paper conveyance. For noise reduction, an effect can be expected only by employing a DC motor. However, for accurate conveyance, an advanced stop control technique and mechanical accuracy are necessary.
To stop a DC motor, the motor is basically powered off when the rotation of a roller has reached a target position, thereby stopping the motor by inertia.
To ensure stop accuracy in use of a DC motor, deceleration before stop and removal of disturbance torque before stop (i.e., stable low-speed operation immediately before stop) are indispensable. When the motor is powered off at a constant and sufficiently low speed, the settling time and stop accuracy until stop can be stabilized.
However, it is very difficult to stabilize the acceleration required time in main scanning (CR) to a completely same value in all driving modes or stabilize the settling time in sub-scanning (LF) to a completely same value in all driving modes.
A serial printer requires cross control to increase the processing speed. In this control, timings are managed such that main scanning driving starts before sub-scanning driving is ended, and sub-scanning stops just when main scanning has reached the printing region, in consideration of an expected value of each time value required for printing.
In this arrangement, it is difficult to accurately estimate the expected time because of a variation in acceleration required time in main scanning and a variation in settling time in sub-scanning driven by the DC motor. Hence, without time management with a sufficient margin for errors of expected time, main scanning reaches the printing region while sub-scanning is still operating, resulting in skew printing.
On the other hand, if the margin is too large, cross printing control becomes ineffective, resulting in low processing speed. That is, in executing cross control in a serial printer that employs a DC motor as a driving source, the highly efficient cross control and skew printing avoidance have a contradictory relationship.
The above problem and ideal operation to be realized by the present invention will be briefly described below with reference to FIGS. 1A to 1C.
FIG. 1A is a timing chart showing the sub-scanning (LF) driving pattern. Reference numeral 21 denotes a sub-scanning driving profile. Due to a variation in control system, the time from the start to stop of driving varies to T_1, T_2, and T_3 in driving three times.
FIG. 1B is a timing chart showing the main scanning (CR) driving pattern. Reference numeral 22 denotes a main scanning driving profile; and 23, a printing region. Due to a variation in control system, the time from the start of driving to the start of printing varies to T_4, T_5 , and T_6 in driving three times.
FIG. 1C is a timing chart showing a driving pattern in cross control printing using the sub-scanning driving pattern shown in FIG. 1A and the main scanning driving pattern shown in FIG. 1B. FIG. 1C simply and clearly shows the concept of the present invention. As is apparent from the history in the past, the best balance can be obtained by determining the degree of overlap between main scanning (LF) and main scanning (CR) by the worst conditions in cross control, i.e., T_3 (the moving time in the slowest profile until the end of movement of LF) and T_4 (the printing start time in the profile with the least margin from the start of movement to the start of printing of CR). If the degree of overlap is increased, skew printing is supposed to occur. If the degree of overlap is decreased, a wasteful main scanning idle interval in which main scanning driving does not overlap sub-scanning driving and no printing is executed is supposed to be generated.
The present invention has been proposed to solve the conventional problems, and has as its object to realize the optimum balance between the sub-scanning driving time and the main scanning driving time in cross control. A printing apparatus and printing control method according to the present invention are mainly characterized by the following arrangements. That is, according to the present invention, a printing apparatus comprises: first storage means for recording a history of a sub-scanning settling time; second storage means for recording a history of a main scanning acceleration required time; supposed settling time determination means for obtaining a supposed settling time in a next sub-scanning driving cycle on the basis of the history information of the sub-scanning settling time stored in the first storage means; supposed idle time determination means for obtaining a supposed idle time from a next start of main scanning driving to a start of printing on the basis of the history information of the main scanning acceleration required time stored in the second storage means; determination means for determining using the supposed settling time and the supposed idle time whether cross control in which main scanning driving starts before an end of sub-scanning driving can be executed in next print scanning processing; and time difference determination means for determining a time difference from a start of sub-scanning driving to the start of main scanning driving using the supposed settling time and the supposed idle time on the basis of determination by the determination means in order to execute cross control in a next print scanning cycle.
Preferably, in the printing apparatus the first storage means stores the sub-scanning settling times in N sub-scanning driving cycles in the past as the history information, and the supposed settling time determination means employs a maximum value stored in the first storage means as the supposed settling time in the next sub-scanning driving cycle.
Preferably, in the printing apparatus, the second storage means stores the main scanning acceleration required times in M main scanning driving cycles in the past as the history information, and the supposed idle time determination means employs a minimum value stored in the second storage means as the supposed idle time in the next main scanning driving cycle.
Preferably, in the printing apparatus, the time difference determination means employs, as the time difference, a time value obtained by adding a predetermined margin time to a time value obtained by subtracting the supposed idle time from the supposed settling time.
Preferably, in the printing apparatus, only when the supposed settling time is shorter than a preset allowable maximum settling time, the determination means determines that cross control can be executed.
Preferably, in the printing apparatus, when the supposed settling time exceeds a preset allowable maximum settling time, the determination means inhibits cross control.
Preferably, in the printing apparatus, when the supposed settling time exceeds a preset allowable maximum settling time, the determination means switches to control for starting main scanning operation after an end of sub-scanning operation.
Preferably, in the printing apparatus, upon powering on, the supposed settling time determination means employs, as an initial condition, a maximum sub-scanning settling time in the history information of the sub-scanning settling times of the N cycles in the past from the first storage means.
Preferably, in the printing apparatus, upon powering on, the supposed idle time determination means employs, as an initial condition, a minimum main scanning acceleration time in the history information of the main scanning acceleration times of the M cycles in the past from the second storage means.
Preferably, in the printing apparatus, the first storage means stores the history information of the sub-scanning settling times of the N cycles in the past in correspondence with each printing condition, and the supposed settling time determination means employs a sub-scanning settling time of a corresponding printing condition as an initial condition in accordance with a print instruction.
Preferably, in the printing apparatus, a DC motor is employed as a main scanning and sub-scanning driving source.
Preferably, in the printing apparatus, the apparatus further comprises first measurement means for measuring a variation in load on a carriage, and the history information of the main scanning acceleration required time stored in the second storage means is initialized on the basis of a measurement result from the first measurement means.
Preferably, in the printing apparatus, the apparatus further comprises second load measurement means for measuring a load variation of a printing medium on a convey mechanism, and the history information of the sub-scanning settling time stored in the first storage means is initialized on the basis of a measurement result from the second load measurement means.
Preferably, in the printing apparatus, the history of the sub-scanning settling time and the history of the main scanning acceleration required time are stored in a nonvolatile memory, and the pieces of information can be held even after power-off.
Preferably, in the printing apparatus, when control is executed by feedback using only speed information without using any position information, the determination means inhibits cross control.
According to the present invention, a printing control method of controlling the printing apparatus comprises: a first storage step of recording a history of a sub-scanning settling time of the printing apparatus in a memory; a second storage step of recording a history of a main scanning acceleration required time of the printing apparatus in a memory; a supposed settling time determination step of obtaining a supposed settling time in a next sub-scanning driving cycle on the basis of the history information of the sub-scanning settling time stored in the first storage step; a supposed idle time determination step of obtaining a supposed idle time from a next start of main scanning driving to a start of printing on the basis of the history information of the main scanning acceleration required time stored in the second storage step; a determination step of determining using the supposed settling time and the supposed idle time whether cross control in which main scanning driving starts before an end of sub-scanning driving can be executed in next print scanning processing; and a time difference determination step of determining a time difference from a start of sub-scanning driving to the start of main scanning driving using the supposed settling time and the supposed idle time on the basis of determination in the determination step in order to execute cross control in a next print scanning cycle.
According to the present invention, a printing control program, which causes a computer to function to control a printing apparatus, comprises: first storage means for recording a history of a sub-scanning settling time; second storage means for recording a history of a main scanning acceleration required time; supposed settling time determination means for obtaining a supposed settling time in a next sub-scanning driving cycle on the basis of the history information of the sub-scanning settling time stored in the first storage means; supposed idle time determination means for obtaining a supposed idle time from a next start of main scanning driving to a start of printing on the basis of the history information of the main scanning acceleration required time stored in the second storage means; determination means for determining using the supposed settling time and the supposed idle time whether cross control in which main scanning driving starts before an end of sub-scanning driving can be executed in next print scanning processing; and time difference determination means for determining a time difference from a start of sub-scanning driving to the start of main scanning driving using the supposed settling time and the supposed idle time on the basis of determination by the determination means in order to execute cross control in a next print scanning cycle.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.